The present invention relates to a hydraulically driven viscous material pump. More particularly, the present invention relates to a hydraulic system which allows a concrete pump to pump in both a long stroke and short stroke mode.
Concrete pumps are used in a variety of applications in the construction field. Particularly, concrete pumps are used when the concrete must be placed in an area that is physically difficult to approach with a ready mix truck. Due to the nature of concrete, the pump must be rugged and wear resistant, and the flow of concrete must be as continuous as possible. Often, concrete pumps attempt to move the concrete at least every ten minutes and with clearing of the lines being required for stops over thirty minutes to an hour depending on the temperature and the concrete admixture.
Certain types of concrete, such as shotcrete and gunite, are shot at a high velocity under pressure, most often by using air, onto a form or other surface. Shotcreting has been used where a relatively thin section of concrete is needed, such as in shell roofs, walls, tanks, chimneys, swimming pools, jacuzzis, and cover and repair applications for all types of structures. Shotcrete is applied in layers of an inch to an inch and a half thick, with the total thickness of up to four inches being obtained by successive placements. With advances in equipment, admixtures and mix designs, many jobs that have traditionally been form and pour are now being shotcreted.
Normally applying standard types of concrete and applying shotcrete require two entirely different types of concrete pumps to apply the material. As a result, contractors are forced to have two kinds of pumps if they wish to apply shotcrete and also work with standard concrete. Requiring two pumps greatly increases the cost to the construction company.
The present invention is an improved dual cylinder material pump for pumping relatively viscous materials such as sludge or concrete. The invention can be operated in two modes, a long stroke mode and a short stroke mode. The concrete pump comprises two material cylinders having movable material pistons on piston rods inside. Connected to each material cylinder is a hydraulic cylinder which drives the hydraulic pistons located on the end of the piston rods opposite the material pistons. The pump operates using reciprocating piston rods so that as the piston rod in one material cylinder is retracting, material is drawn into the material cylinder. At the same time, the other piston rod is extending and material is extruded from the material cylinder. An output valve mechanism is used in conjunction with the synchronized piston rods to ensure a constant outflow of concrete.
The long stroke mode involves extending the hydraulic pistons in the hydraulic cylinder almost the entire length of the hydraulic cylinder. The second mode has a short length stroke which is approximately half the length of long stroke. The selection of the stroke length can be done manually by the pump operator. The benefit of the pump having two stroke lengths is that it allows the pump to operate at maximum efficiency under different operating conditions. The short stroke mode is used in shotcreting applications and has a better cylinder fill efficiency rate. The long stroke mode is used in regular concrete applications, where cylinder fill efficiency can be lower.
The change to the short stroke mode is effected by a valve which changes the volume of flow of hydraulic fluid to the hydraulic cylinders driving the pistons. In addition, two logic signal hydraulic valves monitor the position of the piston in the cylinder. When the piston reaches the short stroke valve, the short stroke valve signals a reciprocating cylinder valve to switch the flow of hydraulic fluid from one cylinder to the other. The short stroke valve also signals the output valve mechanism to change states.